How would "Sunny 16" be applied at altitude, at the equator?

Discussion in 'Exposure Discussion' started by Loren Sattler, Apr 29, 2018.

  1. Loren Sattler

    Loren Sattler Subscriber

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    I was shooting Tmax 100 today at ASA50 on an outing in Equador at 11,000 ft altitude with a Nikon F2 with a yellow filter at mid day. The weather was cloudy, no shadows which would be a 3-4 stop increase from sunny 16. With heavy clouds (no shadows) the meter in my F2 was indicating f8 at 1/60th shutter speed when I expected it to read about f4 at that speed. This was about a two stops difference (underexposed) from the "sunny 16" rule. Note, I confirmed the F2 readings with my cell phone app. Note, I did not remove the yellow filter for metering.

    I usually shoot film near sea level. Should I expect 2 stops more light in these conditions due to high altitude and mid day shooting at the equator? Any experience out there in these conditions?
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    Much more UV. You have to compensate for this about every 10,000 ft.

    PE
     
  3. etn

    etn Subscriber

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    I guess a yellow filter should block UV? Or am I completely wrong?
    Thanks,
    Etienne
     
  4. AgX

    AgX Member

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    It would block too much blue. The 1A should be the better choice.
     
  5. Old-N-Feeble

    Old-N-Feeble Subscriber

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    ETN, I think you're correct that metering through the filter should prevent, or mostly negate, the meter reading being affected by UV. All I can say is, 'sunny-16' is a only starting point... but you already know this. Your supposition that altitude and sun angle affect scene brightness is at least partially correct. What I'm unsure of is if 'altitude' affects scene brightness, when UV is filtered out. I think it might but I honestly don't know.

    EDIT: I just did a very cursory look for affects of altitude on astrophotographic imagery but didn't find anything specific in the couple of minutes I spent looking. I'd think if anyone would know, it would be those folks.
     
    Last edited: Apr 30, 2018
  6. tedr1

    tedr1 Member

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    I seem to recall that the atmosphere absorbs about 50% of incident visible radiation at the surface compared to above the atmosphere in space, for overhead sun. This is a loss of one stop.
     
  7. ic-racer

    ic-racer Member

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    You can look up the various parameters (including latitude) for empiric exposure determination in tables and use a convenient equation to calculate the exposure. (From American Emergency Standard, Photographic Exposure Computer, ASA Z38.2.2--1942)

    description.jpg
     
  8. BrianShaw

    BrianShaw Member

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    Yay, arithmetic! Back in the 1800s there were tables of relative exposure based on time o day and latitude. But I never saw this standard that gives nonrelative values. Thanks for letting me learn something new today!
     
  9. Photo Engineer

    Photo Engineer Subscriber

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    I repeat.... Kodak made 3 HA filters for UV absorbtion. One is the 2B or 2E for ground level. The others were HA1, HA2, and HA3, each intended for 10,000 ft increments in altitude. Beyond that, things were up in the air. I discussed this with two astronauts trying to clarify things. At present, NASA has answers above this altitude.

    PE
     
  10. Alan Edward Klein

    Alan Edward Klein Member

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    Sunny 16 rule works between 10am and 2pm when the sun is high. Season of year and geographic latitude also effect the rule.
     
  11. guangong

    guangong Subscriber

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    Alan is quite correct. As I recall from something read many decades ago, sunny 16 is specific for the mid latitudes, since that was where most people who were using cameras lived. Higher and lower latitudes required adjustments. Also seasons of the year. That’s why light meters were invented.
     
  12. Old-N-Feeble

    Old-N-Feeble Subscriber

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    All true, but how much does 'altitude' affect exposure if UV is filtered out? :smile:
     
  13. AgX

    AgX Member

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    These were special filters for aerial surveying. They are are not to obtain off the shelf in standard filter mounts.
     
  14. Photo Engineer

    Photo Engineer Subscriber

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    They do answer the question posed regarding exposure though.

    And, to some extent, they can be gotten if needed.

    PE
     
  15. AgX

    AgX Member

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    Yes, as those are gelatin filters you are basically right.
     
  16. Stephen Benskin

    Stephen Benskin Member

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    An example of changes of Illuminance with latitude.

    ANSI Exposure Guide 0 and 90 degrees.jpg
     
  17. Photo Engineer

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    Now if you could just include color temperature and UV content vs altitude......
     
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